Futon frame



FIG. 1 is a top view of my ornamental design for a futon frame;

FIG. 2 is a left side view thereof;

FIG. 3 is a right side view thereof;

FIG. 4 is a bottom view thereof;

FIG. 5 is a front view thereof;

FIG. 6 is a rear view thereof; and,

FIG. 7 is a perspective view thereof. 

The ornamental design for a futon frame, as shown. 